Scientists accidentally discover a genetic code that breaks the rules of life
Scientists accidentally discovered a microscopic organism with a genetic code that breaks a rule researchers thought was nearly universal. While testing a new DNA sequencing technique, they examined a previously unknown protist collected from a freshwater pond at Oxford University. To their surprise, the organism uses two genetic signals that normally mark the end of a gene to encode two entirely different amino…
Key points
- Scientists accidentally found a protist, Oligohymenophorea sp. PL0344, whose genetic code reassigns two stop signals to different amino acids.
- The discovery was published in PLOS Genetics in October 2023 after a routine DNA sequencing test on a pond organism.
- Follow-up research in December 2024 found similar independent genetic code changes in several other ciliate species.
A routine experiment on a microscopic organism from a freshwater pond led scientists to an unexpected genetic discovery. The protist, previously unknown to science and named Oligohymenophorea sp. PL0344, was found to read DNA instructions in a way never documented before, challenging a long-held assumption about the genetic code.
The discovery was published in PLOS Genetics in October 2023. Dr. Jamie McGowan, then a postdoctoral scientist at the Earlham Institute, made the finding while testing a DNA sequencing method on a protist collected from a pond at Oxford University Parks in England.
How the unusual code works
In most organisms, the signals TAA and TAG tell cells to stop making proteins. In this protist, both had taken on new roles, encoding two different amino acids: TAA specified lysine and TAG specified glutamic acid. TGA remained the organism's only conventional stop codon.
The researchers also found specialized transfer RNA genes linked to the reassigned codons, supporting that the unusual code was real and not a sequencing error. An unusually high number of TGA stop codons after protein-coding sequences may act as a backup if the ribosome reads past the intended end of a protein.
It's sheer luck we chose this protist to test our sequencing pipeline, and it just shows what's out there
— Dr. Jamie McGowan
More surprises in other ciliates
In December 2024, McGowan and colleagues published further findings in PLOS Genetics. They identified three previously uncultivated ciliate species, from Arctic and Southern Ocean samples linked to the TARA Oceans project, in which UAG appeared to specify leucine instead of acting as a stop signal.
Two additional ciliates, Hartmannula sinica and Trochilia petrani, appeared to use UAG for glutamine. Evolutionary comparisons suggested these changes arose independently at least three times, showing the two signals do not always evolve together.
